(1) Field of the Invention
This invention relates to an inhaler by means of which a solid substance in particulate form, in particular a pharmacologically active substance, can be introduced into the inhaled air of the user of the inhaler.
(2) Description of the Prior Art
Various types of such inhaler are known, one of which is disclosed in German Pat. No. 845385 (and equivalent U.K. Pat. No. 654860) granted to Abbott Laboratories. In the Abbott device a supply of solid material in the form of a fine powder is provided in a capsule having a mesh screen at the lower end. The capsule is adapted to be inserted into the device in such a manner that its lower part projects into a chamber communicating with an air inlet via an inlet tube bent to form approximately a semicircle. An air outlet is provided in the form of a mouthpiece or the like. A ball is located in the inlet tube and is moved during inhalation by the flow of the inhaled air towards the end of the inlet tube, whereby the ball strikes against the capsule and causes a small amount of solid material to fall through the screen of the capsule and to enter the airstream.
A major drawback of the device just described is that it is suitable only for dispensing a relatively large quantity of material, which means that the material in the capsule has to comprise a large amount of an inert carrier in addition to the active substance. This means that it requires many inhalations to transport such an amount of solid material, and it may take from 5 to 10 minutes for a user to inhale sufficient air to take in the required dose of the active substance. This is unacceptable in many cases, particularly where inhalation is intended to relieve conditions which require immediate treatment, such as the conditions prevailing in an asthmatic attack.
Furthermore, because of its shape, the device described above is rather unwieldy and is too large to be conveniently carried around in a bag or pocket. Finally, too much handling is required on the part of the user to prepare for use, i.e. insertion of the capsule into the device after removal of a cap sealing the screen (at which point there is a dnager of loss of solids through the scrren) and the need for correct positioning of the device during inhalation.
It should be mentioned at this point that some, though not all, of the disadvantages referred to above are shared by other forms of known inhaler. In particular, all inhalers presently on the market are relatively large in size and, as a consequence of their expense, all are intended for repeated use.